Ultraviolet irradiation induces cyclooxygenase-2 expression in keratinocytes

We examined the effect of ultraviolet (UV) irradiation on the expression of cyclooxygenases in cultured HaCaT keratinocytes and in human skin in vivo. UVB irradiation (10 and 50 mJ/cm(2)) and hydrogen peroxide (200 mu mol/L) increased cyclooxygenase-2 mRNA expression in HaCaT keratinocytes. No clear expression of cyclooxygenase-1 mRNA was detected in either control or stim ulated HaCaT cells. Genistein, a tyrosine kinase inhibitor, suppressed both the basal and stimulated expression of cyclooxygenase-2 in HaCaT cells. UV B-induced cyclooxygenase-2 mRNA expression was partly inhibited by the anti oxidant N-acetylcysteine and by H-7, a non-specific inhibitor of protein ki nase C. Solar-simulated irradiation (40 mJ/cm(2)) was found to induce in vi vo both cyclooxygenase-2 mRNA and protein expression in human skin, whereas the expression of cyclooxygenase-1 mRNA remained at the basal level. Our r esults show that cyclooxygenase-2 expression is induced by UV irradiation a nd suggest that tyrosine kinases and reactive oxygen intermediates are invo lved in this induction of cyclooxygenase-2.